Fuel cells electrodes and other articles, which are basically matrices of carbon fiber and a binder such as phenolic resin, for a variety of reasons, desirably are of uniform density. In the particular case of fuel cell electrodes, if the fabrication process results in regions of the substrate being too high in density, it is a problem. More particularly, at the completion of the processing, when the electrode substrate is placed in service, overly dense regions may restrict the diffusion of oxygen or hydrogen gas. Thus, the performance of the fuel cell may be impaired.
In the case of aircraft structural part substrates, such as airframe parts, uniformity of density is desirable because it translates into uniformity of strength per unit measure of material.
Currently, there is no easily applied method to nondestructively test resin bonded carbon fiber substrates such as fuel cell electrodes except to visually inspect them. Upon examination, small areas can be tested. However, the present invention solves a particular problem in infrared imaging by creating a steady state temperature gradient around areas of high density. Other methods of heating produce temperature gradients in a transient state making it very difficult to capture and record an infrared image for analysis. More generally, the present invention improves the diagnostic value of infrared imaging of carbon composites over that of eddy current testing and ultrasonic testing.